C135 PCS 7 (PCS7)
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Troubleshooting WinCC Process Trend Freezes and New Year Time Rollover Issues in PCS 7

Troubleshooting WinCC Process Trend Freezes and New Year Time Rollover Issues in PCS 7

When SIMATIC PCS 7 WinCC and SICAM operator stations experience frozen process trends across a New Year transition, the failure is caused by system time synchronization discrepancies or future-dated archive segments. If server or client clocks diverge or if an incorrect date was temporarily set during year-end maintenance, Tag Logging creates database segments stamped in the future. WinCC Online Trend Control cannot plot curves between disjointed timestamps, resulting in flatlines. To resolve this, verify domain time synchronization in the WinCC Time Synchronization editor and reset corrupted TagLogging Fast and Slow archives.

Table of Contents

Executive Summary

In continuous automation plants utilizing SIMATIC PCS 7 and power monitoring systems like SICAM, seamless historical archiving depends on sub-millisecond plant-wide clock synchronization. During year-end rollover periods or manual time adjustments, operator stations frequently exhibit symptoms where real-time trends function normally, but historical archive trends stop updating or display flat horizontal lines. This occurs when local server clocks step backward after previously creating future-dated SQL database segments, or when time synchronization between OS Servers and SICAM gateways fails. This guide diagnoses time rollover faults, outlines diagnostic log analysis, and details archive restoration procedures.

Architectural and System Mechanics

WinCC Time Synchronization and Tag Logging Architecture:

  • Central Clock Synchronization (Time Synchronization Editor):
  • One node on the plant bus (typically the active AS controller or a dedicated SICLOCK GPS master) acts as the time transmitter.
  • OS Servers and Clients act as time receivers, synchronizing their internal clocks using SIMATIC protocol or Network Time Protocol (NTP).
  • Tag Logging Segmentation Mechanics:
  • Historical process values are written into cyclic database archives (TagLogging Fast for high-frequency tags <= 1 min, TagLogging Slow for slower tags).
  • Each segment covers a specific time slice (e.g., 1 day or 1 week). If the station clock jumps ahead (e.g., to next year or future months) and writes data, an archive segment with a future end-timestamp is locked into the Microsoft SQL Server database catalog.
  • Trend Control Display Logic: When the clock is set back to actual time, WinCC queries the archive. The trend control interpolates a straight line between the current point and the future record, causing the curve to appear completely frozen until the real-world time exceeds the future timestamp.

Step-by-Step Engineering and Implementation Procedure

Step 1: Inspect WinCC Diagnostic Log Files

  1. On the affected WinCC OS Server, navigate to C:/Program Files (x86)/Siemens/WinCC/diagnose/.
  2. Open WinCC_Sys_01.log and search for time jump warnings: Time jump backward detected or CCArchiveManager: invalid timestamp.
  3. Open PMTool.log to check performance monitor messages regarding database write stalls.

Step 2: Validate Time Synchronization Settings

  1. Open WinCC Explorer on the OS Server.
  2. Open the Time Synchronization editor.
  3. Verify that 'Synchronization via terminal bus' or 'Synchronization via plant bus' is active.
  4. Ensure that all OS Servers, OS Clients, and SICAM gateways reference the identical master time source.
  5. Open Command Prompt and execute w32tm /query /status to confirm Windows time service synchronization.

Step 3: Identify Future-Dated Database Archive Segments

  1. In the project directory on disk, navigate to the ArchiveManager/TagLoggingFast and TagLoggingSlow folders.
  2. Inspect the filenames of the .mdf and .ldf archive database files.
  3. Check whether any file timestamps or filenames reflect dates in the future.

Step 4: Reset TagLogging Fast and Slow Archives

If future segments exist, reset the archive buffer to restore real-time logging:
1. In WinCC Explorer, expand Tag Logging.
2. Right-click Archive configuration -> TagLogging Fast -> select Archive reset.
3. Confirm the warning dialog.
4. Repeat the procedure for TagLogging Slow -> Archive reset.
5. Restart WinCC Runtime; trends will begin logging immediately from the current timestamp.

Verification

To verify trend restoration:
1. Open Graphics Runtime on the OS Client.
2. Navigate to a process screen containing an Online Trend Control.
3. Toggle between 'Online Tag' and 'Archive Tag'; confirm that the trend curve plots dynamically with real-time updates.
4. Confirm that new .mdf files in ArchiveManager carry current UTC timestamps.

Limitations and Operational Precautions

Operational precautions:
- Executing an 'Archive reset' purges the current short-term database segments from the local OS Server. If long-term history is required, ensure data was previously exported to Process Historian or CAS.
- Never change operating system dates on a running WinCC Server in production; any time shift backward disrupts alarm logging sequences and batch tracking.
- When synchronizing PCS 7 with third-party gateways (e.g., SICAM), always use UTC as the base time standard.

Engineer FAQ

Q: Why did trends freeze after the New Year?

A: The system clock was likely desynchronized, or a backward time jump occurred after a future-dated record was written to the Tag Logging database.

Q: Why does WinCC draw a straight horizontal line in trends?

A: WinCC Trend Control interpolates linearly between data points. A gap between the current time and a future timestamp results in a continuous flat line.

Q: What tool manages time synchronization in PCS 7?

A: The WinCC Time Synchronization editor coordinates time distribution across plant bus and terminal bus nodes.

Q: Where are WinCC diagnostic logs located?

A: Under C:/Program Files (x86)/Siemens/WinCC/diagnose/.

Q: Does an archive reset delete historical data in Process Historian?

A: No. Process Historian maintains its own independent SQL archive and is unaffected by local WinCC short-term archive resets.

Technical References

Related Articles

Related Tags

Tag Logging, Time Synchronization, Trend Freeze, WinCC Archive Reset, New Year Rollover

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